A conventional glow plug for a diesel engine will be described with reference to FIG. 9.
As is well-known, the glow plug 101 is used to, for example, pre-heat a diesel engine and includes a sheath heater 102 and a tubular metallic shell 103 that surrounds the radially outer side of the sheath heater 102.
The sheath heater 102 includes a metal sheath tube 104; a heating element 105 disposed inside the sheath tube 104; insulating powder 106 that fills the interior of the sheath tube 104 so as to surround the heating element 105; a rod-shaped lead 107 inserted into the sheath tube 104 from its rear end and having a front end connected a rear end portion 105r of the heating element 105; and a seal member 108 formed of, for example, silicon rubber and positioned within a seal portion 104a at the rear end of the sheath tube 104 to hermetically seal the gap between the sheath tube 104 and the lead 107.
In the sheath heater 102, after the heating element 105 and the lead 107 are disposed in the sheath tube 104 and the sheath tube 104 is filled with the insulating powder 106, the seal member 108 is attached to the seal portion 104a, and then the sheath tube 104 is swaged to have a predetermined reduced diameter (see Patent Document 1).